This invention relates generally to intravitreal surgical techniques uitilizing the direct application of a laser beam into the vitreous cavity. In particular, this invention relates to the use of a surgical instrument for vitreous surgery employing a CO.sub.2 laser probe incorporating illumination of and viewing from within the eye. This surgical instrument also includes the capability of aspiration for removal of vitreous material together with the maintenance of intraocular pressure by means of irrigation.
This invention is related to a co-pending application entitled "Articulated Arm Radiation Guide" filed by T. J. Bridges and A. R. Strnad on the same day as this application, Ser. No. 338,871.
The prior art is replete with a number of concepts together with reports in the scientific literature evidencing limited instances of actual use of a CO.sub.2 laser in ophthamalic procedures. The use of lasers as surgical tools, and in particular, CO.sub.2 laser systems to accomplish simultaneous cutting and cauterization, is now well established. Cutting action, a result of intense local heating of the tissue due to absorption, occurs when the focused laser beam impinges on the tissue. Cauterization occurs simultaneously due to heating. The beam's energy is absorbed by the medium and will not propagate through it.
The use of a CO.sub.2 laser, operating at 10.6 .mu.m wavelength, offers both advantages and disadvantages in surgical procedures. CO.sub.2 lasers have been particularly useful for the treatment of biological tissue reached by surface application of the radiation directly onto the area affected. Typical uses are dermatological, laryngological and gynecological polyp excisions. The use of a CO.sub.2 laser for the treatment of tissue located within an absorbing medium has, however, to date been generally unsuccessful. This is because the laser radiation at 10.6 .mu.m is completely absorbed by the fluid or tissue that it first impinges. That is, the beam will not penetrate through layers of tissue without first vaporizing or damaging those outer layers. It is for this reason that CO.sub.2 laser techniques have heretofore found application in surface procedures.
The characteristic of complete absorption of the CO.sub.2 laser beam's energy does however find unique application in vitreous surgery. This microsurgery poses requirements for exact cutting of vitreoretinal membranes and elimination of hemorrhage in situ at a precise point within the spherical vitreous cavity. Present intravitreal techniques for the removal of vitreous hemorrhage and cutting vitreoretinal adhesions have utilized two approaches for entry into the vitreous cavity. One, transcorneal, utilizes a corneoscleral incision and the removal of the crystalline lens. The second, trans pars plana, utilizes an instrument which is inserted through the ocular coates, at a point behind the lens. Following removal of hemorrhagic vitreous and reattachment of the retina, the vitreous cavity is, where necessary, filled with normal saline, human vitreous or other suitable fluid such as Ringers. Vitreous surgery utilizes mechanical cutters and suction probes to remove vitreous hemorrhage and/or cut vitreoretinal membranes. Existing surgery frequently requires manipulation of the vitreoretinal bands resulting in secondary vitreous hemorrhage. The technique is performed utilizing an operating microscope or indirect ophthalmoscope.
The two techniques referred to above have traditionally utilized various mechanical cutting instruments. Vitrectomy instruments currently in actual use are conventionally either motor, air or solenoid driven. Rotary, oscillatory or guillotine-like cutters have been developed. The essential concept of each is cutting and removal of the vitreous material from the eye with suction and the replacement of aspirated vitreous with infusion fluid. A hallmark deficiency of such mechanical cutting is that the opening is not at the tip of the probe and thus cutting action is limited when operations take place close to the retinal surface. Such cutting instruments are also objectionable since they place added traction on the vitreoretinal membrane at the point of attachment to the retina as a result of shear during the cutting operation. Accordingly, there is a propensity of retinal tears and hemorrhage during such mechanical cutting.
Another disadvantage of the trans pars plana and transcorneal approaches using mechanical cutters is the inability to control hemorrhage within the vitreous cavity. This deficiency is especially complicated in the case of damaged or leaking vessels of diabetic patients. It is well established that vitreous hemorrhage is a frequent complication of diabetic retinopathy and retinal detachment. Once vitreous hemorrhage has occurred, adhesions develop between the retina and the vitreous body. These adhesions form adhesive bands similar to scars which tend to contract and cause traction on neighboring retinal blood vessels and the retinal tissue itself. The consequence is subsequent vitreous hemorrhage and retinal detachments frequently leading to complete blindness.
The pars plana incision requires viewing of the procedure using an operating microscope positioned above the eye and through a corneal contact lens. Accordingly, there is loss of visibility of the cutting instrument as it approaches the posterior region of the vitreous cavity in a case of massive vitreous hemorrhage. Moreover, if a cataract is present, viewing is impaired.
This deficiency in prior art vitreous procedures becomes further complicated when the hemorrhage may be so dense that the surgeon cannot adequately differentiate a neovascularized vitreoretinal membrane from retinal tissue with its normal vascular supply. Internal illumination by means of fiber optics has generally been developed; however, there is no instrument which currently allows a surgeon to view as well as illuminate the operative site from within the vitreous cavity. Accordingly, while significant advances have occurred in vitreous surgery, significant problems remain.
In response to these problems, the use of a CO.sub.2 laser for simultaneously accomplishing both photo-transection and photocoagulation has been proposed as a cutting tool. A second unique advantage of a CO.sub.2 laser operating at 10.6 .mu.m is its absorption by almost all biological tissue at the point of contact. While this characteristic may be a deficiency in other procedures, it is a material advantage in vitreous surgery since little damage to neighboring or remote ocular tissue occurs. The propensity for damage to retinal tissue is minimized. The problem of propagation through the vitreous cavity, striking the optic nerve is eliminated. Fine et al, in "Preliminary Observations on Ocular Effects of High-Power, Continuous CO.sub.2 Laser Irradiation", Am. J. Ophth. 64:209, August 1967 report that utilizing CO.sub.2 laser radiation on the cornea resulted in little effect on underlying ocular structures. Data By Karlin et al in "CO.sub.2 Laser in Vitreoretinal Surgery", Ophthamology 86:290, February 1979 indicates that the depth of penetration of 10.6 .mu.m radiation is about 10 microns. This minimal depth of penetration is in direct contrast to laser radiation occurring in the visible spectrum, for example, in argon and ruby lasers where propagation occurs through the vitreous over long distances potentially damaging the retina and the optic nerve. Given the high absorption at the point of contact, the CO.sub.2 laser beam can therefore be used to achieve simultaneous cutting and coagulation while other types of lasers cannot. In vitreous surgery, this advantage minimizes the possibility of hemorrhage when neovascular membranes are severed, a problem common in current mechanical cutters.
Investigations have already attempted to determine the feasibility of utilizing a CO.sub.2 laser in vitreoretinal surgery. One report, Karlin et al, supra. investigates four potential applications of this technology. These applications include photo-transection and photocoagulation, intravitreal biopsy, full thickness sclera-chorioretinal wall resection and, radiation effects on the lens. Other reports in the literature such as Campbell et al, "Laser Photocoagulation of the Retina", Tr. Am. Acad. Ophth. Otolaryng. 70:939, November-December 1966; Miller et al, "Transvitreal Carbon Dioxide Laser Photocautery and Vitrectomy", Tr. Am. Acad. Ophth. Otolaryng. 85:1195, November 1978 indicate that evaluation of CO.sub.2 lasers for vitreal surgery have taken place. To date, however, those reports and experiments have been done utilizing rudimentary instruments primarily concerned only with investigating photo-transection and photocauterization. The development of a CO.sub.2 laser instrument capable of widespread ophthalmic clinical use has yet to be achieved.
The definition of such an instrument requires a careful matching of surgical requirements with the level of engineering and scientific knowledge necessary to actually build the device. Hence while the surgeon can define his goals, the level of engineering know-how has not to date been sufficient to achieve them. Laser power requirements, precise focus, minimum instrument size, levels of illumination and field of view angles are all problems that remain.
The prior art is also replete with patents describing laser instruments that conceptually find utility for eye surgery. One, L'Esperance, Jr., U.S. Pat. No. 3,982,541 relates to the use of a CO.sub.2 laser probe coupled to a laser source by means of articulated couplings. One probe configuration utilizes a series of circumferential segmented chambers for the introduction of a stabilizing fluid to maintain eye inflation, that is, an irrigation channel, and an aspiration channel to evacuate debris. The probe size is unacceptably large.
This patent perceives that a fiber optic bundle can be utilized in place of the articulated segments each having mirror elements, given the propagation losses in such articulated arms. However, in such a case, the CO.sub.2 laser cannot be utilized and the patent affirmatively recognizes that some other type, such as argon, should be utilized. Accordingly, the U.S. Pat. No. 3,982,541 patent perceives the difficulties of transmitting CO.sub.2 10.6 .mu.m radiation through fiber bundles.
U.S. Pat. No. 4,122,853 also relates to laser photocautery for use in vitreous surgery. A CO.sub.2 laser is utilized in combination with an articulated arm having mirrored joints. The probe is inserted in the pars plana region to a depth where the tip contacts the vascular tissue to be cauterized. A number of probe embodiments are shown, with the embodiments shown in FIGS. 9-11 of the U.S. Pat. No. 4,122,853 patent having a laser light guide tube 34, an irrigation channel 45, an aspiration channel 78, and, an illuminating light conduit 44. The particular embodiment shown in FIGS. 9-11 of the U.S. Pat. No. 4,122,583 patent does not provide for fiber optic viewing. However, this patent in FIG. 4 perceives an endoscope-like embodiment utilizing simultaneous illumination and viewing. Moreover, while five functions are shown in the various probe configurations of the U.S. Pat. No. 4,122,583 reference, they are not combined into a single functional unit.
An important criterion for probe configuration is to reduce the size to minimize trauma to the eye occasioned by large incisions. The probe should also match the geometry of the incision. Probes having a gauge greater than an 18-20 gauge hypodermic needle are considered unsuitable for vitreous procedures. Given this requirement for minimization of cross-sectional size, the optimization of the probe presents one area of continuing research. If the cross-sectional size is decreased, it becomes increasingly difficult to provide adequate illumination at the probe end. Problems of cold light and laser beam attenuation become significant and, when coupled with insufficient resolving power in the optic viewing segment tend to render those combined features unworkable. Such problems are compounded in the case of procedures within the vitreous cavity where the field of view is frequently clouded by hemorrhage.
Another problem not adequately addressed in prior art systems is the power loss attendant to transmission of the laser beam from the laser to the probe. This problem is particularly acute in the case of CO.sub.2 lasers where absorption occurs at the point of contact. Hence, special arrangements are necessary to transmit a CO.sub.2 laser beam along an irregular path.
U.S. Pat. No. 4,170,997, is directed to this problem and relates to a laser for surgical applications and specifically, a CO or a CO.sub.2 laser having illumination through fiber bundle 13 and viewing through fiber optic bundle 16. An axial hollow tube 18 contains a flexible infrared transmitting fiber optical waveguide 19 coupled to a laser source 20. An aiming or target beam produced by HeNe laser is utilized with transmission selectively coupled by means of an optical shutter 22 interposed in the path of the CO.sub.2 laser beam.
An important problem in the delivery of infrared laser radiation is the provision of a flexible radiation path between the laser source and the non-fixed probe. In the prior art, a number of solutions have been suggested. Among them are conventional articulating arms, as in U.S. Pat. No. 4,122,853 and illustrated in Herriott, "Application of Laser Light", Scientific American, 219, 144 (1968); flexible metal waveguides in Garmire et al, "Low Loss Propagation and Polarization Rotation in Twisted Infrared Metal Waveguides", Appl. Phys. Letters 34(1), 35 (1979); and infrared transmitting fibers in Pinnow, U.S. Pat. No. 4,170,997; Pinnow et al, "Polycrystalline fiber Optical Waveguides for Infrared Transmission", Appl. Phys. Letters 33(1), 28 (1978); Bridges et al, "Single-Crystal AgBr Infrared Optical Fibers", Optics Letters 5, 85 (1980). These techniques all have serious difficulties.
In both metal waveguides and infrared fibers, as known in the art, the guides are multimode. The single mode radiation from the laser, when launched, rapidly degrades into a multimode pattern. The pattern changes in form and the beam wanders as the guide is moved to follow movements of the probe. Hence, the beam does not remain centered, a critical factor in ophthamalic surgery. Such degradation considerably reduces the maximum intensity that can be obtained by focusing the output radiation.
Prior art articulating arms while preserving the single mode suffer from alignment problems. Unless the input beam is precisely launched on axis and the arm mechanism is precisely correct, the output beam will wander in a complicated manner as the arm is manipulated. In the context of a surgical procedure this is unacceptable. Moreover, such arms have heretofore been large and cumbersome making them unsatisfactory linkages for hand-held probes.